Why are black people a constant target?

I think a big part of it is politically motivated. Since racial identity politics has become the new moral outrage from liberals in the US, conservatives (because let's face it, they're mostly the ones dismissing black people) automatically adopt a contrarian attitude in order to reconcile with their knee-jerk assumption that liberals are automatically wrong.

The other part of it is most likely the availability heuristic. The weird thing about anti-minority attitudes is that it almost always comes from people that live in the most homogeneous places. Like the example you brought up about China. How many of them actually know any black people?

When your only exposure to something is what you see in entertainment or in social media, which by design amplify stereotypes and negativity, then these people's exposure to racial differences is largely an illusion constructed by compounding biases. It's essentially propaganda. As a result, people on the internet have become fully indoctrinated into hating groups of people they've never met or had any interactions with.

While there is something to be said about crime and criminality being statistically concentrated in predominantly black neighborhoods, there are a variety of other factors plaguing those communities besides skin color. To extrapolate such egregiously generalized claims from such a narrow slice of the population is the hallmark of ignorance.

It would be like believing most men will assault you or that many white boys will grow up to commit a mass shooting. What you see in the world of media is not necessarily reflective of the real world. They just exaggerate things in order to capture your attention. To believe that black people are inherently criminal because of a few bad neighborhoods in America is such a simpleton point of view. It speaks volumes as to how little you've actually seen of the world.